As the evolution of batteries continues, and particularly as lithium batteries become more widely accepted for a variety of uses, the need for safe, long-lasting, high-energy batteries becomes more important. There has been considerable interest in recent years in developing high energy density cathode-active materials for use in high energy primary and secondary batteries. For example, lithium-sulfur based materials can reach a specific capacity equal to 1670 mAh/g, which is one order of magnitude higher than for LiCoO2. Unfortunately, lithium sulfur batteries have traditionally suffered from low sulfur utilization resulting in a low capacity and severe capacity fade, resulting in short battery lifetimes. Additionally, lithium sulfur batteries are typically operated in the molten state, thus high temperature operation is needed. The poor cycleability of lithium sulfur batteries is mainly due to its insulating character and the solubility of intermediary polysulfides during the charge-discharge process.
Lithium selenium batteries, using molten salt eutectics such as LiF—LiCl—LiI (see U.S. Pat. No. 3,488,221) or a mixture of LiAlO2 and LiF—LiCl—LiI eutectics (see U.S. Pat. No. 3,666,500), have been described, but which operate only in the molten state of the salt, at high temperature (e.g. above 285° C.). A battery based upon Li2Se/Li was also investigated using a fluidic positive electrode (e.g. 1M Li2Se in a mixture of ethylene carbonate and ethyl methyl carbonate (volume ratio 1 to 1)) (see U.S. Pat. No. 7,645,539). However, neither of these approaches is of practical use due to the extreme operating temperatures and safety issues of liquid or molten electrodes.